Mechanical Ventilation (MV) is a common treatment in the ICU. The main difference is the positive pressure administrated to the lungs instead of the negative pressure in spontaneous breathing. The positive pressure applied in the alveoli causes a local and systemic inflammatory response. Lung injuries are well described due to MV. Some studies relate changes in the Intracranial Pressure (ICP) and Cerebral Perfusion Pressure (CPP) with the Positive End- Expiratory Pressure in neurological patients. Also changes in the MCA velocity have been described with MV. The studies speculate that the changes are related to the intrathoracic positive pressure. However, all studies are in patients with acute neurological pathology.